$setDifference

Definition

Returns values from the first set absent from the second.

Expression operator · Sets · Studio Visual: available. Studio validates the complete expression separately.

Syntax

{ "$setDifference": [ <array>, <other> ] }

Replace angle-bracket placeholders with expressions or values.

Optional parameters may be omitted.

Parameters

Parameter	Required	Description
array	Yes	Expression supplying the source array.
other	Yes	Expression supplying the other array for the set operation.

Arguments are positional: keep the order shown. The authoring signature accepts 2–2 arguments.

Behavior

The following observations use the example expression below. Each row substitutes one argument while retaining the other example arguments. A missing field differs from an explicit null; the result shown is what Core actually returned.

For the array argument:

Input case	Supplied value	Result
null	null	Error — Expected array.
missing	Field absent	Error — Expected array.
decimal	2.5	Error — Expected array.
numeric string	"12"	Error — Expected array.
text	"hello"	Error — Expected array.
boolean	true	Error — Expected array.
typed date	{"$date":"2026-01-15T15:00:00Z"}	Error — Expected array.
empty array	[]	[]
numeric array	[1,2,3]	[1]
object	{"x":1}	Error — Expected array.

Argument handling

Invocation	Result
{"$setDifference":[]}	Error — $setDifference requires exactly two arrays.
{"$setDifference":{"unexpected":1}}	Error — $setDifference requires exactly two arrays.

Examples

Expression:

{
  "$setDifference": [
    [
      1,
      2
    ],
    [
      2,
      3
    ]
  ]
}

Input document:

{}

Observed SrotaX result: [1].

Detailed input cases

Expand the complete argument-by-argument test matrix

Each table changes only the indicated argument from the example above. Other arguments retain their baseline values. Values normally come from the input field probe; literal configuration arguments are replaced directly. “Missing” means the field is absent, not explicitly null. Numeric strings are strings, not numbers.

Argument: array[0]

Input case	Supplied value	SrotaX result
null	null	Error — Expected array.
missing	Field absent	Error — Expected array.
zero	0	Error — Expected array.
negative	-2	Error — Expected array.
decimal	2.5	Error — Expected array.
numeric string	"12"	Error — Expected array.
text	"hello"	Error — Expected array.
empty string	""	Error — Expected array.
boolean	true	Error — Expected array.
false	false	Error — Expected array.
typed date	{"$date":"2026-01-15T15:00:00Z"}	Error — Expected array.
decimal128	{"$numberDecimal":"1.25"}	Error — Expected array.
empty array	[]	[]
numeric array	[1,2,3]	[1]
mixed array	[1,null,"x",3]	[1,null,"x"]
nested array	[[1,2],[3]]	[[1,2],[3]]
empty object	{}	Error — Expected array.
object	{"x":1}	Error — Expected array.
ISO date string	"2026-01-15T15:00:00Z"	Error — Expected array.

Argument: other[1]

Input case	Supplied value	SrotaX result
null	null	Error — Expected array.
missing	Field absent	Error — Expected array.
zero	0	Error — Expected array.
negative	-2	Error — Expected array.
decimal	2.5	Error — Expected array.
numeric string	"12"	Error — Expected array.
text	"hello"	Error — Expected array.
empty string	""	Error — Expected array.
boolean	true	Error — Expected array.
false	false	Error — Expected array.
typed date	{"$date":"2026-01-15T15:00:00Z"}	Error — Expected array.
decimal128	{"$numberDecimal":"1.25"}	Error — Expected array.
empty array	[]	[1,2]
numeric array	[1,2,3]	[]
mixed array	[1,null,"x",3]	[2]
nested array	[[1,2],[3]]	[1,2]
empty object	{}	Error — Expected array.
object	{"x":1}	Error — Expected array.
ISO date string	"2026-01-15T15:00:00Z"	Error — Expected array.

Verification

This page records 41 executed cases. It covers individual argument substitutions, not every cross-product of arguments, locale, daylight-saving transitions, numeric overflow, collation or resource limits. No untested behavior is guaranteed.

Download exact expressions, inputs and SrotaX results. Errors are observed messages, not stable public error codes. The reference generator reads the checked-in execution report; do not edit generated observations by hand.

MongoDB differences

Compared with MongoDB 9.0.4: 9 exact BSON matches, 28 both rejected, 4 value/type/acceptance differences, 0 object-field-order differences.

“Exact” includes numeric BSON types and object key order. A value of 3 as int32 differs from 3.0 as double. Object-field-order differences are reported separately; object key ordering is not enforced by the engine regression baseline. Both rejected does not mean the error codes or messages match. This is finite-case evidence, not full compatibility certification.

Show observed differences

Tested case	SrotaX	MongoDB
array[0] / null	Error — Expected array.	null
array[0] / missing	Error — Expected array.	null
other[1] / null	Error — Expected array.	null
other[1] / missing	Error — Expected array.	null

Download full comparison evidence.